In recent years, for example, in a manufacturing process of a semiconductor device, the diameter of a semiconductor wafer (hereinafter, referred to as a “wafer”) increasingly becomes larger. Further, the wafer is required to be thinner in a specific process such as mounting. When a thin wafer with a large diameter is transferred or subjected to polishing as it is, warpage or break can occur in the wafer. Therefore, in order to reinforce the wafer, for example, bonding the wafer to a wafer being a supporting substrate or a glass substrate is performed. The predetermined processing such as polishing and the like are performed on the wafer with the wafer being joined with the supporting substrate as described above, and then the wafer and the supporting substrate are separated from each other.
The separation of the wafer and the supporting substrate from each other is performed using, for example, a separation apparatus. For example, Patent Document 1 proposes a separation apparatus that directly joins a wafer having devices formed thereon to a supporting substrate having a thermally oxidized film formed thereon and then separates the wafer. The separation apparatus has, for example, a first holder that holds the wafer, a second holder that holds the supporting substrate, and a nozzle that jets liquid between the wafer and the supporting substrate. Then, this separation apparatus separates the wafer and the supporting substrate from each other by jetting liquid from the nozzle to between the wafer and supporting substrate joined together, namely, to a joint surface between the wafer and supporting substrate, at a jetting pressure greater than the joint strength between the wafer and the supporting substrate, preferably, a jetting pressure twice or greater than the joint strength.    [Patent Document 1] Japanese Laid-open Patent Publication No. H9-167724